Concentric drill and drill press for use therewith



, J- H. CAMPBELL Filed April 8, 1952 INVENTOR.

CONCENTRIC DRILL AND DRILL PRESS FOR USE THEREWITH Dec. 25, 1956 U d]States P e This inventionrelates to compound concentric twist drills andto a drill press for operating drills.

2,775,148 Patented Dec. 25, 1956 ice Fig. 4 is a side view of the outerdrill member on the O shank 11 having tongues 12. The drill member is Itis well recognized that the revolutions perminuteat which a drill may berun depends, to a large extent, upon its peripheral speed. Assuming thatthe peripheral speed of a drill should not exceed sixty fe'etper minute,the most practical speed, for running a one-quarter inch drill is 900revolutions per minute while a corresponding one inch drill would have225 revolutions per minuteas its most practical speed. H :With a oneinch drill, the drilling of the one-quarter inch central core of the oneinch hole takes correspondingly longer than thedr'illing ofa quarterinch hole with a quarter inch drill. This is dueto two factors of whichone is the substantially higher rate of rotation practicable with thequarter inch drill and the other is the size of the web at the cuttingpoint which separates the lands.

The major objective of this invention is to enable holes to be morerapidly drilled relative to their diameter and, in accordance with theinvention, there is provided a compound drill comprising a first drillmember having an axial bore extending from end to end thereof, and asecond drill member in the bore and rotatable relative to the firstdrill member. The second drill member is of such length that its pointand the end of its shank are exposed beyond the corresponding ends ofthe first drill member.

The invention also relates to a drill press for use with such concentricdrills and in a drill press, in accordance with the invention, there isa first spindle member having an axial passageway extending from end toend thereof in which asecond spindle member is located to rotaterelative to the spindle member. The drill receiving end of the secondspindle member is disposed in predetermined position relative to thedrill receiving end of the first spindle member and the other end of thesecond spindle member protrudes beyond the other end of the firstspindle member. The drill press includes a drive to rotate one of thespindle members and a gear connection between said members is providedto rotate the. other spindle member at a different rate of speed.

In accordance with the invention, the inner and outer drill members maybe rotated at their most practical speeds. This enables the feed to beaccelerated with substantial savings resulting in time, labor, andexpense, because the central core is removed by the inner drill memberwhich has a higher rate of rotation than the outer drill member andbecause the retarding effect of the web is reduced to a minimum sincethe size of the web is approximately proportioned to that of a drill.

In the accompanying drawings, there is shown an illustrative embodimentof the invention from which its several novel features and advantageswill be readily apparent.

In the drawings:

Fig. 1 is a vertical section of the head of a drill press,

Fig. 2 is a side view of the inner drill member, on an enlarged scale,

Fig. 3 is a similar view but with the inner drill turned 90,

provided with an axial bore 13 extending from end to end thereof and isso formed, as will be apparent from Fig. 6, that the bottomof each flute14 is arcuate with respect to the drill axis. With respect to the lands15, the drill member 10 may be said to have a tubular core 16. Thecutting point 17 tapersinwardly and intersects the bore 13. By way ofcontrast, the conventional twist drill has a solid web intermediate itslands which at the cutting point .presents such an obtuse angle, say tothe work, as to efiect cutting by an inefiicient scraping action. Thisimpediment to drilling becomes particularly objectionable .and has arelatively long shank 19 to enable the cutting point 20 to protrudebeyond the cutting point 17 of the drill member 10 when the extremity ofthe shank 19 is exposed beyond the extremity of the shank 11. The drillmember 18 is also provided with a groove 21 extending from end to end ofits shank 19 and opening into one of the flutes 22. The groove 21 may beused for the delivery of a coolant or lubricant between the drillmembers to the work.

In Fig. 1 there is shown a drill press head as illustrative of means bywhich the drill members 10 and 18 may be separately supported androtated at different relative speeds.

The drill press frame 23 supports a pair of vertically spaced bearings24 and 25. A drive pulley 26 has a sleeve 27 entrant of the bearing 24and provided with an annular groove 28 to receive the retainer 29 shownas threaded through the -bearing 24.

A housing 30 includes a sleeve 31 slidably supported by the bearing 25to be raised and lowered on rotation of the shaft 32 by the lever 33through gearing, conventional The spindle member 34 has a tapered socket39 atits lower end to receive the shank 11 of the outer drill member 10.The socket 39 opens into an axial bore 40 and at 41 is shown thetransverse slot which receives the tongues 12 of the outer drill member10. The other end of the spindle member 34 has a cylindrical socket 42also opening into the axial bore 40 to provide an axial passageway forthe second or inner drill member 18.

The socket 42 also serves to receive one end of the second spindlemember 43 which has an axial bore 44 extending from end to end thereofand a splineway 45 for the spline 46 fixed in the pulley 26 and theslidable key 47. The second spindle member 43 is provided with a chuck48 to receive and anchor the extremity of the shank 19 of the innerdrill member 18.. The shank 19 extends through the bore 44 with thecutting point 20 protruding beyond the cutting point 17' of the drill 10carried by the first spindle member 34.

cordance with the: invention.

JThenhousingiBdhas -vertically.-alined bossesxSZ rotatably supportingthe spindle ;53';adapted to be turned .by; the manually operated armv*54 r and including an iec- I lcentric portion 1 55 for the gears 56:and'aSTaWhich-mesh respectively, whenthe -armr54 is in thC'rPOSitlOIlshown tin'aFig.M1,:Withi1h6gpil1i0l1t49 landtthe gearz35. When :thedrill .-press'- is to be :used with *a conventional :twistdrill,1the-:arm --54ris turned ft-hereby to-disengagethe gear connectionbetween f-thexspindle members and the :key 547 -iss then. depressed: tointerconnectithe spindle members for direct drive.

2111' practise, .the ,-flutesof the". inner- .drill :member 18=are'short' beingv preferablyyof'a length: not exceeding twice the drilldiameter. "Itsshank; however, vis gof:substantial length in order thatit may extend throughthe'chuck .48toenable itscuttingv point toxbepositioned. as desired :relative to the cutting point ofuthe outer drill10.

nm-From-vthe foregoing, it will beappreciated thatcom pound concentricdrills and drill: presses and the likeinJaCcQrdance-Withztheinventionsare well adapted to acaccelerate theboringoft. lar esize holesv inmetal withsattendant saving of time, labor andcosts.

What I therefore claim and desire to secure by Letters Patent is: I

In a drill press for use with concentric drills, a first spindle memberfor the outer drill and having an axial bore extending from end toeiidithereof, a second spindle memberthaving onesend entrant of saidthere and rotatablerelativeto said, first spindle-member, said secondspindle member having an aXial bore, said bores in said membersreceiving-theinherit-drill, the otherien'd of said second spindle memberbeingrexposed, means engageable with"'s'aid"expo'sedend to'rotate one ofsaid second members, a gear; fast-Jon-each..of said spindle members, anoperator control to lock the gear on the first spindle to the gear onthe second spindle, a rotatable spindle including an eccentric, anoperator control to turn said eccentric .betweenwifirst' and secondpositions, and gears rotatable together relative toisaid spindle and inthe; first position of said eccentric meshing with: respective onesiofusaid spindle memberigears.

', References-Cited in the file of this patent ,UNITED STATES PATENTS2,390,744 asmith Dec. 11, 1945

